City Comptroller John Liu is not going to let the federal investigation into his campaign fund-raising dampen his 45th birthday.

The mayoral hopeful is planning a fund-raiser Monday for his big day — where he’ll eschew his self-imposed $800-per-donation cap. “We are asking people to contribute up to the [$4,950] maximum, like all candidates,” said campaign spokesman George Arzt.

The birthday bash’s “host committee” includes labor bigwigs and elected officials, but many said they won’t attend or donate.

Liu “asked if he can use my name” and “I told him he could, but I won’t be able to make it,” said Brooklyn’s Democratic Party boss, Assemblyman Vito Lopez. Another “host,” Senate Minority Leader John Sampson, also won’t attend.